1. Field of the Invention
The present invention relates to an optical fiber array for holding a light transmission member such as optical fiber at a predetermined position.
More particularly, the present invention relates to an optical fiber array to be sealed in a package of a holding device of the light transmission member together with an optical element connected to the light transmission member.
2. Description of Related Art
Conventionally, it has been well known that an optical fiber array for fixing an optical fiber that is a light transmission member and connecting the optical fiber to another member uses a support substrate having a fixing groove such as V groove formed in a plurality of arrays. On the support substrate, an optical fiber in which wires each having a ribbon shaped cover removed therefrom are housed and arranged in fixing grooves is held and fixed on an upper substrate. Then, this optical fiber array is coupled with other optical parts, for example, light emitting diode or light receiving elements, or is optically coupled with other optical fibers or rod lenses. As a method for forming the fixing groove, an etching technique is applied to a silicon substrate so as to fit a material for the support substrate or a grinding technique is applied to an optical glass or a ceramics substrate.
In a substrate of any material as well, if an optical axis of an optical fiber fixed between the support substrate and the upper substrate deviates from a predetermined position, a transmission loss between the optical fiber and another light transmission means increases. Therefore, it is required to achieve very high processing precision of the fixing groove on an optical fiber support substrate, for example, 0.5 micron or less. Thus, as means for fixing the support substrate and the upper substrate, there has been means for fixing an optical fiber into a V groove with a resin based adhesive. In addition, in order to avoid degradation of light emitting characteristics caused by adhering of an organic gas generated from a resin based adhesive to a light emitting interface of a light emitting diode, the above means has been improved to means for fixing the optical fiber in the V groove by way of soldering. Further, the diameter of an optical fiber is about 125 micron. If a solder is supplied from a distal end face of the support substrate into the V groove with its very small gap between the V groove and the optical fiber, a gap in which a solder is not supplied in the gap between the V groove and the optical fiber is likely to occur. Thus, the above means has been improved to means in which the light transmission member is housed in the groove, a solder sheet is placed on the groove and light transmission member, this solder sheet is heated while it is pressurized toward the groove via the upper substrate, whereby a solder is supplied into the gap between the groove and the light transmission member
However, even in an optical fiber array in which the support substrate and the upper substrate are fixed to each other by means of a solder sheet, a solder wets in a longitudinal direction faster than the solder wetting and being filled in the peripheral direction of an optical fiber forming a metalized layer. Thus, for example, in the case where the upper substrate is pushed down suddenly, if a remaining gap extends long along the groove without the solder being filled sufficiently in the fixing groove, an inert gas wets through the gap in the groove. Thus, there has been an apprehension that air tightness of a package or case for preventing degradation of optical elements such as laser cannot be maintained.
Namely, the above package or the like housing an optical fiber array is often subjected to severer exterior environment. That is, such package or the like is subjected to a high temperature of 60xc2x0 C. or to a low temperature of xe2x88x9240xc2x0 C. or is subjected to extremely dry environment or humid environment. Thus, the optical fiber must operate constantly for a long time under such severe ambient environment. If a gap remains in the solder in the groove as described previously, the air remaining in this gap repeatedly expands and contracts, thereby moving the peripheral solder or moisture entering the gap. Therefore, the fixing position of the optical fiber slightly changes under the influence of such expansion and contraction. If the fixing position of the optical fiber is changed, even if such change is slight, the optical axis deviates from an optical axis of the optical element, and thus, a coupling loss increases or changes.
It is an object of the present invention to provide an optical fiber array for fixing a light transmission member such as optical fiber at a predetermined position, wherein each transmission member can be securely fixed into a groove by using a solder, and a gap between the light transmission member and the groove is unlikely to occur.
According to a first aspect of the present invention, there is provided an optical fiber array comprising: a support substrate for housing a light transmission member in a fixing groove; and an upper substrate for holding the light transmission member, said optical fiber array being sealed in a package of a holding device of the light transmission member together with an optical element connected to the light transmission member with air tightness, wherein a light transmission member at which a metalized layer is not formed is housed in a fixing groove of the support substrate at which the metalized layer is formed, and is soldered by the upper substrate at which the metalized layer is formed.
In this manner, the support substrate and upper substrate each having the metalized layer formed thereon are fixed to each other by being bonded with a solder wetting along the metalized layer. The light transmission member pinched therebetween is free of any metalized layer, is free of force of bonding with a solder, and is fixed by the pinching force from both faces. On the other hand, a solder surrounding the peripheral face of the light transmission member is small in wettability relevant to the light from the light transmission member, and is free of bonding force. Thus, before the solder wets along the light transmission member, it is pressed by the force of pinching between the support substrate and the upper substrate, moves in the peripheral direction, and is filled inside of the fixing groove. Therefore, no gap is provided between the light transmission member and the groove so that air tightness of a package or case for preventing degradation of an optical element such as laser could be held reliably. In addition, the array position of the optical fibers could be fixed. Thus, unlike a conventional example, there does not occur an increase or change of a coupling loss because the optical axis of the optical fiber deviates from that of the optical element.
The light transmission member is preferably an optical fiber, and may be a passive light transmission member such as rod lens. Although no particular limitation applies to an optical element optically coupled with the light transmission member, a laser light emitting element for oscillating laser light or a light receiving element for receiving laser light are preferable.
In addition, with respect to the surface roughness Ra of a light transmission member at which a metalized layer is not formed, an optical fiber array of 0.1 to xe2x88x921 micron is preferable. In this manner, if the surface roughness is smaller than 0.1, bonding force weakens due to a change with time, and the fixing position of the optical fiber is displaced. Thus, there is an apprehension that deviation from the optical axis of the optical element occurs, thus causing an increase or change in coupling loss. On the other hand, if the surface roughness is greater than (1, the wettability of solder increases. Thus, there is a possibility that the solder moves in a longitudinal direction faster than solder filling in the peripheral direction, and air tightness is degraded in a gap in which the solder is not filled.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.